1. Field of the Invention
The present invention relates to control apparatuses for electric vehicles.
2. Description of the Related Art
As an example of a conventional electric vehicle, an electric wheelchair is disclosed in Japanese Unexamined Patent Application Publication No. 10-99378. According to this publication, the electric wheelchair is moved by both an operation force applied by a caregiver who pushes and pulls the vehicle and a driving force generated by a motor based on the operation force. The direction and amount of the operation force are detected by operation force detecting means provided in handles, and when the amount of operation force applied by the caregiver exceeds a predetermined value, the driving force is generated by the motor. The operation force detecting means may also be installed in handrims provided along the circumference of wheels.
In the above-described electric wheelchair, the operation force detecting means detects the operation force applied either on the handles by the caregiver or on the handrims by the occupant, and the driving force is provided by the motor based on the result of the detection. Accordingly, on upward slopes, for example, a driving force in the forward direction is provided by the motor in accordance with the operation force applied, so that the load on the operator is reduced. In addition, when the operator applies the operation force in the reverse direction on downward slopes, a driving force in the reverse direction is generated by the motor so as to prevent acceleration of the electric wheelchair. Accordingly, the load on the operator is reduced.
However, in the above-described conventional electric vehicle, when the operator wishes to maintain a certain speed on a downward slope, it is difficult to establish an adequate balance between gravity, which tries to rotate the wheels in the forward direction, and the force applied by the motor, which tries to rotate the wheels in the reverse direction. As a result, the operation force varies, so that the movement of the vehicle cannot be adequately controlled.
Accordingly, in view of the above-described problems, an object of the present invention is to provide a control apparatus for an electric vehicle which ensures the stability of the operation force even on slopes and which improves the operability of the electric vehicle.
According to one aspect of the present invention, a control apparatus for an electric vehicle having wheels driven by motors, the control apparatus comprises an operation force detecting unit which detects a direction and an amount of an operation force applied to the electric vehicle by an operator; a rotational direction detecting unit which detects a rotational direction of each wheel of the electric vehicle; and a control unit which controls each motor such that the motor generates a driving force in accordance with the operation force detected by the operation force detecting unit and that, when the control unit determines that the rotational direction of each wheel detected by the rotational direction detecting means is opposite to the rotational direction corresponding to the direction of the operation force detected by the operation force detecting means, the motor generates an electrical braking force. In the control apparatus for an electric vehicle which is constructed as described above, the control unit controls each motor such that, when it determines that the rotational direction of each wheel is opposite to the rotational direction corresponding to the direction of the operation force, generates the electrical braking force. Thus, when the operator applies the operation force in the direction opposite to the moving direction of the electric vehicle on a slope, the electrical braking force is generated and the load placed on the operator is reduced. Accordingly, the speed of the vehicle can be controlled without applying a force larger than necessary. As a result, the movement of the vehicle is adequately controlled, and the operability thereof on slopes is improved.
The control unit may increase the electrical braking force as the operation force is increased, the operation force being applied in the direction corresponding to the rotational direction opposite to the rotational direction of the corresponding wheel and being detected by the operation force detecting means. In such a case, the electrical braking force can be adjusted in accordance with the amount of operation force which is applied in the direction opposite to the direction corresponding to the rotational direction of the corresponding wheel. As a result, the operability on slopes can be further improved.
In addition, when the electrical braking force is generated, the control unit may reduce the electrical braking force as the operation force is increased, the operation force being applied in the direction corresponding to the same rotational direction as the rotational direction of the corresponding wheel and being detected by the operation force detecting means. In such a case, the electrical braking force is gradually reduced instead of being set to 0 immediately. Accordingly, safety is ensured and the movement of the vehicle is adequately controlled.
In addition, the control unit may determine the electrical braking force by accumulating a change therein, and the absolute value of the change in the electrical braking force may be increased as the operation force detected by the operation force detecting means is increased. In such a case, since the electrical braking force is immediately increased in accordance with the operation force, the electrical braking force quickly responds to the operation force. Accordingly, safety and quick response of the vehicle are insured.
In addition, the change in the electrical braking force may be 0 when the operation force detected by the operation force detecting means is less than a predetermined value, and, when the operation force detected by the operation force detecting means exceeds the predetermined value, the absolute value of the change in the electrical braking force is increased in accelerating manner as the operation force detected by the operation force detecting means is increased. In such a case, the electrical brake is prevented from responding too sensitively when a small operation force is applied. In addition, since the electrical braking force is increased in accelerating manner in accordance with the operation force, the electrical braking force quickly responds to the operation force. Accordingly, safety and quick response of the vehicle are insured.
In addition, the electrical braking force may have an initial value which is a fixed value. In such a case, the initial electrical braking force is always the same. Accordingly, the operability of the vehicle in the braking operation can be improved.
In addition, the control unit may control the motors for driving right and left wheel such that the motors generate the electrical braking forces independently of each other, and the control unit may gradually increase the smaller one of the electrical braking forces so as to make the smaller one of the electrical braking forces closer to the larger one. In such a case, the coordination between the right and the left wheels can be achieved, and the movement of the vehicle can be adequately controlled.
In addition, control unit may set the electrical braking force to 0 when a state, in which the corresponding wheel is stationary and the operation force detected by the operation force detecting means is less than a predetermined value, is maintained for a predetermined period of time. In such a case, when the vehicle is stopped and then restarted, the electrical braking force is removed so that the vehicle can be easily moved again. Accordingly, the operability of the vehicle is improved.
According to another aspect of the present invention, a control apparatus for an electric vehicle having wheels driven by motors, the control apparatus comprises an operation force detecting means which detects a direction and an amount of an operation force applied to the electric vehicle by an operator; a rotational direction detecting unit which detects a rotational direction and the amount of rotation of each wheel of the electric vehicle; and a control unit which controls each motor such that the motor generates a driving force in accordance with the operation force detected by the operation force detecting unit and that, when the control unit determines that each wheel is rotated by a predetermined amount in a rotational direction and that the rotational direction is opposite to the rotational direction corresponding to the direction of the operation force detected by the operation force detecting unit, the motor generates an electrical braking force. In the control apparatus for an electric vehicle which is constructed as described above, the control unit controls each motor such that, when it determines that the rotational direction of each wheel is opposite to the rotational direction corresponding to the direction of the operation force, generates the electrical braking force. Thus, when the operator applies the operational force in the direction opposite to the moving direction of the electric vehicle on a slope, the electrical braking force is generated and the load placed on the operator is reduced. Accordingly, the speed of the vehicle can be controlled without applying a force larger than necessary. As a result, the movement of the vehicle is adequately controlled, and the operability thereof on slopes is improved. In addition, the electrical braking force is not applied until the corresponding wheel is rotated by a predetermine amount in a rotational direction. Thus, even when the driving wheel temporarily rotates in the reverse direction while it climbs up an upward slope, the electrical braking force is not applied until it rotates by a predetermined amount. Then, when the vehicle starts to climb up the upward slope again, the electrical assist force can be immediately applied. Accordingly, the operability of the vehicle is further improved.
In addition, according to another aspect of the present invention, a control apparatus for an electric vehicle having wheels driven by motors, the control apparatus comprises an operation force detecting unit which detects a direction and an amount of an operation force applied to the electric vehicle by an operator; a rotational direction detecting unit which detects a rotational direction of each wheel of the electric vehicle; and a control unit which controls each motor in accordance with the operation force detected by the operation force detecting unit, and which selectively switches the operation mode for each motor over a driving mode in which the motor generates a driving force in accordance with the operation force detected by the operation force detecting unit, a braking mode in which the motor generates an electric driving force when the absolute value of the operation force detected by the operation force detecting unit is less than the predetermined value, and a downward slope braking mode in which the motor generates an electric braking force when the rotational direction of each wheel detected by the rotational direction detecting unit is opposite to the rotational direction corresponding to the direction of the operation force detected by the operation force detecting unit. In the control apparatus for an electric vehicle which is constructed as described above, the control unit sets the operation mode to the downward slope braking mode when it determines that the rotational direction of each wheel is opposite to the rotational direction corresponding to the direction of the operation force. Then, the motor generates the electrical braking force. Thus, when the operator applies the operation force in the direction opposite to the moving direction of the electric vehicle on a slope, the electrical braking force is generated and the load placed on the operator is reduced. Accordingly, the speed of the vehicle can be controlled without applying a force larger than necessary. As a result, the movement of the vehicle is adequately controlled, and the operability thereof on slopes is improved. In addition, when the absolute value of the operation force detected by the operation force detecting unit is less than the predetermined value, the control unit sets the operation mode to the braking mode and controls the motor such that the motor generates the electrical braking force so as to decelerate the vehicle. Accordingly, when the operation force is removed, the electric vehicle is safely decelerated.
When the control unit switches the operation mode from the downward slope braking mode to the braking mode, the initial electrical braking force generated in the braking mode may be set to the electrical braking force generated in the downward slope braking mode. In such a case, the initial value of the electrical braking force generated in the braking mode is set to the electrical braking force applied in the end of the downward slope braking mode. Thus, the temporary loss of the braking force does not occur immediately after the operation mode is changed.
In addition, when the control unit switches the operation mode from the braking mode to the downward slope braking mode, the initial electrical braking force generated in the downward slope braking mode may be set to the electrical braking force generated in the previous downward slope braking mode operation. In such a case, the initial electrical braking force generated in the downward slope braking mode is set based on the electrical braking force generated in the previous downward slope braking mode operation. Accordingly, the temporary loss of the braking force does not immediately after the operation mode is changed to the downward slope braking mode again.
In addition, when the operation mode is not the downward slope braking mode, and when the control unit determines that the corresponding wheel is rotated by a predetermined amount in a rotational direction and that the rotational direction is opposite to the rotational direction corresponding to the direction of the operation force detected by the operation force detecting unit, the control unit may switch the operation mode to the downward slope braking mode. In such a case, the operation mode is not changed to the downward slope operation mode and the electrical braking force is not applied until the corresponding wheel is rotated by a predetermined amount in a rotational direction. Thus, even when the driving wheel temporarily rotates in the reverse direction while it climbs up an upward slope, the electrical braking force is not applied until it rotates by a predetermined amount. Then, when the vehicle starts to climb up the upward slope again, the electrical assist force can be immediately applied. Accordingly, the operability of the vehicle is further improved.
In addition, the control unit may set the electrical braking in the downward slope braking mode operation based on only the rotational direction of the corresponding wheel detected by the rotational direction detecting unit and the rotational direction corresponding to the direction of the operation force detected by the rotational force detecting unit. Thus, when the vehicle moving down a slope stops and starts to climb up again, the control unit immediately responds and reduces the electrical braking force. Accordingly, the operability is further improved.